In microsystems technology, components having dimensions in the micrometer range act together in systems (MEMS=microelectromechanical systems) for various applications. Such micromechanical systems usually have one or more sensors and actuators, as well as a control electronics system. Compared to conventional “macrosystems”, micromechanical systems above all have the advantages in cost savings (low use of materials, parallel production) and in efficiency (low energy and performance demand enables autonomous systems). In addition, they offer a great functional spectrum, high functional densities, new functionality (integration of electrical and nonelectrical functions). For, because of the integration and miniaturization, new physical effects are able to be utilized, and the short information paths lead to short reaction times. Moreover, they mostly have higher reliability than conventional systems, above all because of the omission of plugs and cables.
The use of micromechanical systems is conceivable wherever sensors and actuators and an electronic system collaborate. One of the greatest application areas is inertial sensors, such as gyroscopes, acceleration and inclination sensors. They are used, among other things, in the automotive area for triggering air bags and for the detection of skidding and rollover. In particular, one or multi-axial micromechanical yaw-rate sensors are used for the most varied applications (in the automotive field, for example, for ESP, navigation and rollover sensing=ROSE; in the consumer field, for instance, for image stabilization, motion detection and navigation). A common form of implementing these sensors uses the Coriolis effect. A mass suspended from springs is set into vibrational motions in a first direction by a drive mechanism, whereby a Coriolis force acts upon the mass when a rotational rate in a second direction is present. This force acts perpendicular both to the drive direction and to the rotational rate present and has the effect of a motion or oscillation of the mass in this third direction.
An acceleration sensor is discussed in DE 195 23 895, which is particularly developed as a Coriolis yaw-rate sensor. In one specific embodiment, the Coriolis yaw-rate sensor is also designed for the detection of linear accelerations. For this purpose, a vibrating structure formed by seismic masses and suspended to move in torsional vibration is given an additional electronic position control, which detects and dampens linear accelerations acting on the vibrational structure. This electronic position control is formed by comb structures, situated on the vibrating masses, which are engaged with additional comb structures, so that, if a voltage is applied, capacitances between the two comb structures are measurable. In response to a deflection of the vibrational structure by a linear acceleration, the distance between the individual fingers of the comb structures changes, whereby a capacitance change sets in which is detected using the position control electronic system. By changes in the voltage applied to the comb structures, it is possible, by electrostatic action, to regulate the distance between the comb structures to a specified setpoint value. The amount of the voltage used for the distance regulation at the same time supplies information on the size of the linear acceleration acting upon the vibrational structure.
To activate yaw-rate sensors, a circuit usually generates periodic voltage curves (such as sine or rectangular pulse), which are then converted via a capacitive drive structure on the sensor into periodic drive forces, which set the structure (i.e. the seismic mass) in vibration. In order to operate the sensor at its mechanical resonant frequency, it is of advantage to select and/or regulate the excitation frequency of the drive force in a suitable manner. At the resonant frequency, no phase shift prevails between the speed of motion of the seismic mass brought about by the drive force and the drive force.
In order for the vibrational amplitude to be controllable, a yaw-rate sensor usually also has elements for detecting the drive motion as well as corresponding control loops in the evaluation circuit. In currently available sensors, this drive circuit takes up relatively great space, however, namely ca. 30 to 40% of the active circuit area.